/* hmac_prng.c - TinyCrypt implementation of HMAC-PRNG */

/*
 *  Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *    - Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *
 *    - Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 *    - Neither the name of Intel Corporation nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

#include "hmac_prng.h"
#include "constants.h"
#include "hmac.h"
#include "utils.h"

/*
 * min bytes in the seed string.
 * MIN_SLEN*8 must be at least the expected security level.
 */
static const unsigned int MIN_SLEN = 32;

/*
 * max bytes in the seed string;
 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
 */
static const unsigned int MAX_SLEN = UINT32_MAX;

/*
 * max bytes in the personalization string;
 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
 */
static const unsigned int MAX_PLEN = UINT32_MAX;

/*
 * max bytes in the additional_info string;
 * SP800-90A specifies a maximum of 2^35 bits (i.e., 2^32 bytes).
 */
static const unsigned int MAX_ALEN = UINT32_MAX;

/*
 * max number of generates between re-seeds;
 * TinyCrypt accepts up to (2^32 - 1) which is the maximal value of
 * a 32-bit unsigned int variable, while SP800-90A specifies a maximum of 2^48.
 */
static const unsigned int MAX_GENS = UINT32_MAX;

/*
 * maximum bytes per generate call;
 * SP800-90A specifies a maximum up to 2^19.
 */
static const unsigned int MAX_OUT = (1 << 19);

/*
 * Assumes: prng != NULL
 */
static void update(TCHmacPrng_t prng, const uint8_t *data, unsigned int datalen, const uint8_t *additional_data, unsigned int additional_datalen) {
  const uint8_t separator0 = 0x00;
  const uint8_t separator1 = 0x01;

  /* configure the new prng key into the prng's instance of hmac */
  tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));

  /* use current state, e and separator 0 to compute a new prng key: */
  (void)tc_hmac_init(&prng->h);
  (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
  (void)tc_hmac_update(&prng->h, &separator0, sizeof(separator0));

  if (data && datalen)
    (void)tc_hmac_update(&prng->h, data, datalen);
  if (additional_data && additional_datalen)
    (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);

  (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);

  /* configure the new prng key into the prng's instance of hmac */
  (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));

  /* use the new key to compute a new state variable v */
  (void)tc_hmac_init(&prng->h);
  (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
  (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);

  if (data == 0 || datalen == 0)
    return;

  /* configure the new prng key into the prng's instance of hmac */
  tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));

  /* use current state, e and separator 1 to compute a new prng key: */
  (void)tc_hmac_init(&prng->h);
  (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
  (void)tc_hmac_update(&prng->h, &separator1, sizeof(separator1));
  (void)tc_hmac_update(&prng->h, data, datalen);
  if (additional_data && additional_datalen)
    (void)tc_hmac_update(&prng->h, additional_data, additional_datalen);
  (void)tc_hmac_final(prng->key, sizeof(prng->key), &prng->h);

  /* configure the new prng key into the prng's instance of hmac */
  (void)tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));

  /* use the new key to compute a new state variable v */
  (void)tc_hmac_init(&prng->h);
  (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
  (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);
}

int tc_hmac_prng_init(TCHmacPrng_t prng, const uint8_t *personalization, unsigned int plen) {
  /* input sanity check: */
  if (prng == (TCHmacPrng_t)0 || personalization == (uint8_t *)0 || plen > MAX_PLEN) {
    return TC_CRYPTO_FAIL;
  }

  /* put the generator into a known state: */
  _set(prng->key, 0x00, sizeof(prng->key));
  _set(prng->v, 0x01, sizeof(prng->v));

  update(prng, personalization, plen, 0, 0);

  /* force a reseed before allowing tc_hmac_prng_generate to succeed: */
  prng->countdown = 0;

  return TC_CRYPTO_SUCCESS;
}

int tc_hmac_prng_reseed(TCHmacPrng_t prng, const uint8_t *seed, unsigned int seedlen, const uint8_t *additional_input, unsigned int additionallen) {
  /* input sanity check: */
  if (prng == (TCHmacPrng_t)0 || seed == (const uint8_t *)0 || seedlen < MIN_SLEN || seedlen > MAX_SLEN) {
    return TC_CRYPTO_FAIL;
  }

  if (additional_input != (const uint8_t *)0) {
    /*
     * Abort if additional_input is provided but has inappropriate
     * length
     */
    if (additionallen == 0 || additionallen > MAX_ALEN) {
      return TC_CRYPTO_FAIL;
    } else {
      /* call update for the seed and additional_input */
      update(prng, seed, seedlen, additional_input, additionallen);
    }
  } else {
    /* call update only for the seed */
    update(prng, seed, seedlen, 0, 0);
  }

  /* ... and enable hmac_prng_generate */
  prng->countdown = MAX_GENS;

  return TC_CRYPTO_SUCCESS;
}

int tc_hmac_prng_generate(uint8_t *out, unsigned int outlen, TCHmacPrng_t prng) {
  unsigned int bufferlen;

  /* input sanity check: */
  if (out == (uint8_t *)0 || prng == (TCHmacPrng_t)0 || outlen == 0 || outlen > MAX_OUT) {
    return TC_CRYPTO_FAIL;
  } else if (prng->countdown == 0) {
    return TC_HMAC_PRNG_RESEED_REQ;
  }

  prng->countdown--;

  while (outlen != 0) {
    /* configure the new prng key into the prng's instance of hmac */
    tc_hmac_set_key(&prng->h, prng->key, sizeof(prng->key));

    /* operate HMAC in OFB mode to create "random" outputs */
    (void)tc_hmac_init(&prng->h);
    (void)tc_hmac_update(&prng->h, prng->v, sizeof(prng->v));
    (void)tc_hmac_final(prng->v, sizeof(prng->v), &prng->h);

    bufferlen = (TC_SHA256_DIGEST_SIZE > outlen) ? outlen : TC_SHA256_DIGEST_SIZE;
    (void)_copy(out, bufferlen, prng->v, bufferlen);

    out += bufferlen;
    outlen = (outlen > TC_SHA256_DIGEST_SIZE) ? (outlen - TC_SHA256_DIGEST_SIZE) : 0;
  }

  /* block future PRNG compromises from revealing past state */
  update(prng, 0, 0, 0, 0);

  return TC_CRYPTO_SUCCESS;
}
